127 research outputs found
Quantum Quench of an Atomic Mott Insulator
We study quenches across the Bose-Hubbard Mott-insulator-to-superfluid
quantum phase transition using an ultra-cold atomic gas trapped in an optical
lattice. Quenching from the Mott insulator to superfluid phase is accomplished
by continuously tuning the ratio of Hubbard tunneling to interaction energy.
Excitations of the condensate formed after the quench are measured using
time-of-flight imaging. We observe that the degree of excitation is
proportional to the fraction of atoms that cross the phase boundary, and that
the quantity of excitations and energy produced during the quench have a
power-law dependence on the quench rate. These phenomena suggest an excitation
process analogous to the Kibble-Zurek (KZ) mechanism for defect generation in
non-equilibrium classical phase transitions
Interacting Stark localization dynamics in a three-dimensional lattice Bose gas
We measure the thermalization dynamics of a lattice Bose gas that is Stark
localized by a parabolic potential. A non-equilibrium thermal density
distribution is created by quickly removing an optical barrier. The resulting
spatio-temporal dynamics are resolved using Mardia's statistic, which is a
measure sensitive to the shape of the entire density distribution. We conclude
that equilibrium is achieved for all lattice potential depths that we sample,
including the strongly interacting and localized regime. However,
thermalization is slow and non-exponential, requiring up to 500 tunneling
times. We show that the Hubbard term is not responsible for thermalization
via comparison to an exact diagonalization calculation, and we rule out
equilibration driven by lattice-light heating by varying the laser wavelength.
The thermalization timescale is comparable to the next-nearest-neighbor
tunneling time, which suggests that a continuum, strongly interacting theory
may be needed to understand equlibration in this system
Does platelet-rich plasma improve patellar tendinopathy symptoms?
Q: Does platelet-rich plasma improve patellar tendinopathy symptoms? Evidence-based answer: IT’S UNCLEAR. High-quality data have not consistently established the effectiveness of platelet-rich plasma (PRP) injections to improve symptomatic recovery in patellar tendinopathy, compared to placebo (strength of recommendation [SOR]: A, based on 3 small randomized controlled trials [RCTs]). The 3 small RCTs included only 111 patients, total. One found no evidence of significant improvement with PRP compared to controls. The other 2 studies showed mixed results, with different outcome measures favoring different treatment groups and heterogeneous results depending on follow-up duration.Emily Wolfenden, MD, MPH; Brian Vukelic, MD; Matthew DeMarco, MD; Jordan Knox, MD (University of Utah, Salt Lake City) Dominik Ose, DrPH, MPH (University of Utah, Salt Lake City)Includes bibliographical reference
Active cancellation of servo-induced noise on stabilized lasers via feedforward
Many precision laser applications require active frequency stabilization.
However, such stabilization loops operate by pushing noise to frequencies
outside their bandwidth, leading to large "servo bumps" that can have
deleterious effects for certain applications. The prevailing approach to
filtering this noise is to pass the laser through a high finesse optical
cavity, which places constraints on the system design. Here, we propose and
demonstrate a different approach where a frequency error signal is derived from
a beat note between the laser and the light that passes through the reference
cavity. The phase noise derived from this beat note is fed forward to an
electro-optic modulator after the laser, carefully accounting for relative
delay, for real-time frequency correction. With a Hz-linewidth laser, we show
dB noise suppression at the peak of the servo bump (
kHz), and a noise suppression bandwidth of MHz -- well beyond the
servo bump. By simulating the Rabi dynamics of a two-level atom with our
measured data, we demonstrate substantial improvements to the pulse fidelity
over a wide range of Rabi frequencies. Our approach offers a simple and
versatile method for obtaining a clean spectrum of a narrow linewidth laser, as
required in many emerging applications of cold atoms, and is readily compatible
with commercial systems that may even include wavelength conversion
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